1. Field of the Invention
This invention relates to a gyro and a method of operating the same. More particularly, the present invention relates to a gyro comprising a ring resonator type laser.
2. Related Background Art
Mechanical gyros comprising a rotor and a vibrator and optical gyros adapted to detect the angular velocity of a moving object are known. Particularly, optical gyros are regarded as real innovation because they can start to operate instantaneously and provide a wide dynamic range. Optical gyros include ring resonator type laser gyros, optical fiber gyros and passive type ring resonator gyros, of which ring resonator type laser gyros comprising a gas laser were developed most early and have been used in aeronautic applications and other applications. Recently, small, high precision, ring resonator type laser gyros have been proposed and Japanese Patent Application Laid-Open No. 5-288556 describes such a gyro.
However, known ring resonator type laser gyros are so designed that a laser beam propagating clockwise and another laser beam propagating counterclockwise are once emitted therefrom to the outside and received by a photodetector, which transforms their optical beat into electric beat as signal. This means that a coupling loss arises when the laser beams enter the photodetector. Additionally, known ring resonator type laser gyros need an optical isolator in order to avoid the noise generated by the beams returning from an external point of reflection to the laser.
Japanese Patent Application Laid-Open No. 4-174317 describes a technique of observing the angular velocity of an object by causing a pair of laser beams to be transmitted circularly clockwise and counterclockwise within the semiconductor laser and utilizing the beat produced by the interference of the laser beams.
A laser device described in the above cited patent document will be described by referring to FIGS. 34 and 35 of the accompanying drawings. FIG. 34 is a schematic plan view of the device and FIG. 35 is a schematic cross sectional view taken along line 35xe2x80x9435 in FIG. 34. Referring to FIGS. 34 and 35, there are shown an InP substrate 10, ridge type optical waveguides 11, 12A, 12B and 12C, total reflection corner mirrors 13A, 13B, 13C and 13D arranged at the four corners, a voltage detection terminal 14 and a bias current supply terminal 15. The total reflection corner mirrors are formed, as shown in FIG. 35, by engraving the surface using an etching technique.
However, the technique described in the above cited patent document cannot provide a high yield when manufacturing such devices on a commercial basis. Further, there is a strong demand for laser devices of the type under consideration that can oscillate with a lower driving power. This invention is made under these circumstances.
Therefore, it is a first object of the present invention to provide a gyro comprising a semiconductor laser that can be driven with a low electric current or a low voltage and a method of operating such a gyro.
Another object of the present invention is to provide a gyro that is totally or almost free from problems such as coupling loss and optical feedback noise and a method of operating such a gyro.
Still another object of the present invention is to provide a compact gyro and a method of operating such a gyro.
According to a first aspect of the invention, the above object is achieved by providing a gyro comprising a ring resonator type semiconductor laser for having laser beams transmitted circularly in opposite directions relative to each other, wherein the angle xcex1 formed by the surface of the active layer of the semiconductor laser and the lateral surface of each of the low refractive index layers sandwiching the active layer and showing a refractive index lower than the active layer satisfies the requirement of 75xc2x0xe2x89xa6xcex1xe2x89xa6105xc2x0 over the entire periphery of the low refractive index layers.
The ring resonator type semiconductor laser can detect the beat signal produced by the rotation of the gyro as a change in the electric current flowing through the semiconductor laser, the voltage applied to the semiconductor laser or the impedance of the semiconductor laser.
Preferably, the surface precision of the lateral surface of each of the low refractive index layers is less than xc2xd of the wavelengths of the laser beams in the active layer.
According to a second aspect of the invention, there is provided a method of operating a gyro comprising a ring resonator type semiconductor laser, wherein the angle xcex1 formed by the surface of the active layer of the semiconductor laser and the lateral surface of each of the low refractive index layers sandwiching the active layer and showing a refractive index lower than the active layer satisfies the requirement of 75xc2x0xe2x89xa6xcex1xe2x89xa6105xc2x0 over the entire periphery of the low refractive index layers, the method using the change in the electric current, the voltage or the impedance as signal for determining the angular velocity of the ring resonator type semiconductor laser.
Preferably, the voltage or the electric current for driving the ring resonator type semiconductor laser is modulated by means of a frequency not found in the frequency band of the signal.
Preferably, a piezoelectric element is used to drive the ring resonator type semiconductor laser to rotate clockwise or counterclockwise.